Polish your axle, make sure your brake bell doesn’t bind on the key, file the setscrew marks off it as you take it off, and use a one-piece sprocket! Two bolts for the hubs, two bolts for the brake bell, two bolts for the sprocket hub, six setscrews, and out it slides. For a 206 three bolts are enough on the sprocket, then slide it all back together and align.
I’ve moved to basically only single cutting sprockets, assuming they are #219. Even with a 50mm axle with the right sprockets the flex back fine, and then you are a lot less likely to deal with the “tight-loose” phenomenon.
The other special sprocket hubs may work, I haven’t tried them. What works for me is to use a sprocket hub that is threaded so they become “studs”. Keeps you from having to use two hands to tighten the nuts. We use a two bolt sliding mount like this Sliding Mount.
A sprocket change consists of;
Loosen the two nuts on the engine mount about a full turn each.
Slide the engine back, the chain will become slack.
Lift the chain off the old sprocket and let it hang down.
Remove the nuts holding the old sprocket using an electric impact gun (we use a Dewalt) Don’t let the impact gun fling the nuts to the stratosphere. Clean the nuts with some brake clean.
Remove the old sprocket, clean it and put it in your sprocket holder. Check the hub for dirt, grit, damage, etc…
Place the new sprocket on the hub making sure the alignment marks are correct.
Start all the nuts back onto the studs on the hub. Do not tighten them down, finger tight is fine.
Lay the chain over the new sprocket and rotate the axle until the split line of the sprocket is straight up and down.
Wearing a glove or using a rag, grasp the top and bottom runs of the slack chain and pull them together. This will make the chain lay across both split line gaps and align the spacing of the sprocket.
While holding the chain like this tighten the sprocket bolts. We use the impact for this - don’t go crazy.
Slide the engine forward to the correct chain tension and tighten the two engine hold down nuts on the sliding mount.
Check the chain for free running and correct tension.
We can change a sprocket this way in about five minutes not counting putting up on the stand or letting it cool off.
Our engine mount has four bolts, the trick to that style is to figure tighten it and then use a cross pattern to slowly tighten each corner just like you do when putting on a head. This prevents the engine from becoming uneven and messing up your chain tension.
It takes me just a few minutes to change a gear most of that is spent reaching for the gear rack. It takes practice to do it quickly.
This has brought me to another thought. Just like the driver the mechanic needs to practice and work on their race craft. A weekends race can be won or lost in the garage on Monday a week before the race when making plans.
The conventional engine mounts that adjust and tighten from the bottom can be a big part of the problem. Some mounts tighten down evenly and square with the axle, others not as well. There are a lot of things welded to the frame right where the mount goes, kicker stubs, frame cross members, bearing hangers, etc… The tube can distort and cause a chronic chain misalignment when the mount is tightened. This is especially critical on low powered classes like LO206 - you can’t afford to waste any! That’s why we went to the sliding mount. You can set up the lower part of the mount to correct any issues with filing, shimming or special torquing procedures. Just make sure the mount is square to the axle. We use a chunk of aluminum, a 123 block and some clamps but just about anything will work. Once the base is good the rest will follow. The sliding mount also makes pulling the engine off for clutch service very easy and quick. Engine Alignment
The advice Benn gave is really good advise. Spending money on a really nice mount is a good investment. Getting alignment is really hard with a crappy mount, especially if your tubes have been squashed a bit from the mount butterfly’s that have two screws vs one big one per butterfly like the odenthal. As far as quick sprocket changes I use the Rocket split gears and they can be used normal with holes but also have these angled slots that allow you to slide them on (rotate on really) without removing the nut. If you have the threaded sprocket hub it’s even easier. Just half turn the nuts, slide off slide on new gear, tighten and go. Same even if you have the chain guard rings. The downfall is the tight loose thing can be big if you don’t seat them well and squeeze them with the chain as you tighten, because you aren’t in the holes rather slots, but it’s not a big problem.
Danny Lemello(s) at Russell’s Karting Specialties, once built a sprocket hub that used a threaded ring to hold the sprockets in place. It used a spanner wrench to tighten the ring. Very quick sprocket changes. His was designed as a chain oil for induro racing, but that didn’t work out. The screw-on sprocket holder worked fine, but the oiler function didn’t. I used one at one time.
Hello Eric - I am setting up a lo206 for the first time on a chassis set up with a clone engine currently. My rear sprocket is brand new and the person / company I bought it from cut it in one place like you mention. It’s 219 I think. Il not sure what that stands for exactly. I’m wondering if it will bend or flex on this one cut so I can fit it over the axle. The axle seems too wide but maybe it’s flexible enough like you mention. Thank you for the help.
Hey Mark! Thank you for reaching out to me on this question!
#219 denotes the type of chain ‘pitch,’ basically the spacing from center-center of the ‘valleys’ between the teeth on the sprocket where the chain will sit / turn. Different sprockets match different chains, which have different chain pitches. For karting in general the #219 chain pitch and #35 chain pitch are the most popular.
Regarding bending over the axle, you should be able to bend the sprocket over the axle and it should return back to form once you do this. It takes a little force, but it is do-able. A handful of sprockets out there won’t return back to form, but these are not the case for most racers / sprocket types. If your axle seems too wide, you may have a 50mm axle, and I know it seems intimidating, but the sprocket will flex and return over these axles.